De Luca, A., and F. Flacco. “Dynamic Gravity Cancellation and Regulation Control in Robots With Flexible Transmissions: Constant, Nonlinear, and Variable Stiffness”. Department of Computer and System Sciences Antonio Ruberti Technical Reports, vol. 2, no. 11, July 2010, https://rosa.uniroma1.it/rosa00/index.php/dis_technical_reports/article/view/8892.